The general production and processing of polymer dispersions [cf. e.g. Encyclopedia of Polymer Science and Engineering, Vol. 8, p. 659ff. (1987); D. C. Blackley, in High Polymer Latices, Vol. 1, p. 35ff. (1966); Emulsion Polymerisation, Interscience Publishers, Inc. (1965), and Dispersionen synthetischer Hochpolymerer, F. Holscher, Springer Verlag (1969) and also Ullmanns Encyclopadie der technischen Chemie, 4th ed., Vol. 19, p. 132ff.], polymer suspensions [cf. e.g. Encyclopedia of Polymer Science and Engineering, Vol. 16, p. 443ff. (1989); High Polymers, Vol. X, Polymer Processes, Interscience Publishers, Inc., p. 69ff. (1956); High Polymers, Vol. XXIX, Polymerization Processes, John Wiley & Sons, Inc., p. 106ff. (1977); Ullmanns Encyclopadie der technischen Chemie, 4. ed., Vol. 19, p. 125ff.] and polymer solutions [cf. e.g. Encyclopedia of Polymer Science and Engineering, Vol. 15, p. 402ff. (1989); High Polymers, Vol. X, Polymer Processes, Interscience Publishers, Inc., p. 175ff. (1956); High Polymers, Vol. XXIX, Polymerization Processes, John Wiley & Sons, Inc., p. 198ff. (1977); Ullmanns Encyclopadie der technischen Chemie, 4th ed., Vol. 19, p. 112ff.] have been described on many occasions in the past and are therefore sufficiently well known to the skilled worker.
The production of polymer dispersions, solutions and suspensions from the corresponding monomer units usually takes place continuously or batchwise in closed reactors. Depending on the monomer units used for the polymerization and the liquid medium used to take up the polymers, the reaction often takes place under an inert gas atmosphere, at elevated temperature, and, if desired, under superatmospheric pressure. After the end of the reaction and after the system has, if appropriate, been let down to atmospheric pressure, with recycling of the monomers, the contents of the reactor, which are often still at temperatures above 20.degree. C., must be transferred from the reactor into a buffer, conditioning or storage container.
So that no subatmospheric pressure is formed within the reactor during the draining or pumping-off process, which would retard the emptying process, it has been suggested to "aerate" the reactor system during the emptying operation and so provide pressure compensation. By aeration (venting) here is meant a process in which the volume of liquid discharged from the reactor is matched by supplying precisely the same volume of inert gas or atmospheric air to the reactor per unit time under given pressure conditions. A similar procedure is adopted when emptying buffer, conditioning and storage containers or other vessels.
Disadvantages which have been found with the aeration of reactors and containers during the emptying process with inert gas or air, however, are that on the inner walls and internals of such vessels deposits and polymeric films of low solubility are formed which reduce the internal volume and run counter to the mode of action of the internals, such as stirrers, flow disruptors, sensors, valve closures, etc., and which act counter to heat transfer in the case of heat exchangers and heating or cooling coils. This means that the corresponding reactors, containers and tanks have to be subjected to extensive cleaning processes at frequent intervals and, furthermore, that it is necessary to cope with production downtime owing to the nonavailability of the units in question during the cleaning operations.
For avoiding deposits, Encyclopedia of Polymer Science and Engineering, Vol. 12, p. 536 (1988) describes spray jets which are permanently installed in the reactor head and from which, during the emptying process, a medium in liquid form is sprayed in as a cleaning fluid, said liquid medium being the same medium which comprises the polymers. Disadvantages which have been found with this technique are that the amount of spray agent required for cleaning undesirably dilutes the dispersion, solution or suspension discharged from the reactor, to a considerable extent, and that the degree of deposit prevention is unsatisfactory.
It is an object of the present invention to provide an improved method of emptying vessels containing dispersions, solutions or suspensions of polymers.